From visual inspection it is also apparent that pulsars in the non-RVM class have significantly more circular polarization (compared to linear polarization) than pulsars with RVM-like swings. To quantify this we determined how many pulsars have \(|V| > L\)  in more than 5 phase-bins across the profile, which we denote as \(V_{\rm h}\)  in Table REF . There are 288 such pulsars, 72% of which occur in the non-RVM class. Expressed another way, pulsars denoted as \(V_{\rm h}\)  occur 16% of the time in the RVM class and 59% in the non-RVM class. It therefore appears as a general, if not hard-and-fast rule, that distortions of the PA swing occur simultaneously with a high degree of circular polarization (see for example PSR J1607–0032 in Figure REF ). Generation of circular polarization has long been a thorny problem in pulsar astronomy [1]}, [2]}. In the simplest picture where two linearly polarized orthogonal modes interact incoherently, neither circular polarization nor distortion of the RVM curve can happen. Recently, [3]}, [4]} pointed out that coherent addition of the modes with some (non-zero) phase lag not only generates circular polarization, but can also reproduce many of the peculiar PA traverses seen in single pulses. Motivated by this, [5]} developed a framework for comparing the polarization properties of a large sample of pulsars to draw conclusions about the ratio of incoherent to coherent mixing (Oswald et al. In Prep.).
